The present invention relates to a circuit for driving electronic devices with a low supply voltage. In particular the invention relates to a circuit for driving a MOS transistor with a low supply voltage which is per se insufficient to drive said MOS transistor.
As is known, the use of switching MOS transistors has some advantages with respect to the use of bipolar transistors. In particular MOS transistors operate at higher switching frequencies because of the absence of the charge storage phenomena, and the driving power of MOS transistor is lower.
In particular this second aspect can be very important when operating with high switching currents.
Despite these advantages it is not always possible to use MOS transistors to drive electrical loads or other circuits, since the gate terminal of MOS transistors requires higher driving voltages than the base terminal of bipolar transistors. In fact, as is known, DMOS transistors for example require a gate driving voltage higher than 3 V, whereas bipolar transistors require a base voltage of 0.7 V.
This is a severe limitation for the use of MOS transistors in systems fed at low voltage.
For the sake of clarity, reference should be made to FIG. 1, illustrating an exemplifying diagram of a usual circuit employing a MOS transistor to drive an inductive load. As can be seen, the MOS transistor, indicated by M1, is connected in series to an inductor L arranged between M1 and the supply voltage V.sub.IN. The circuit furthermore comprises a control stage 1 also connected to the supply voltage and to the gate terminal of the transistor M1 so as to drive said MOS transistor, said stage 1 feeding a gate voltage variable according to the intended switching sequences.
This circuit can operate only if the supply voltage V.sub.IN is at least greater than the threshold voltage V.sub.T of the MOS transistor (which, as mentioned, is equal to 3 V for a DMOS transistor). If the input supply voltage V.sub.IN is lower, the diagram of FIG. 1, cannot be used and the MOS transistor should be replaced with a bipolar transistor, thus renouncing the above mentioned advantages related to the high switching frequencies and to the low power consumption required to drive the transistor.